1. Field of the Invention
The present invention is directed to printing methods wherein a print image carrier, for example paper, is printed upon employment of printing parameters that have been set and predetermined. The invention is also directed to printer devices or, respectively, copier devices for the implementation of the printing or, respectively, copying methods. The printer devices are explained in greater detail below.
2. Description of the Related Art
Printing methods that, for example, work according to the electrographic, magnetographic or some other non-mechanical principle are known. In an electrographic printing method, the printing parameters include the charge potential of the photoconductor, the auxiliary potential in the development station and other physical setting points that influence the printing process.
It is known to set the printing parameters dependent on the light sensitivity, the age or the temperature of a photoconductor employed in the printing. What is achieved by a control of the actual printing parameters is that the predetermined rated printing parameters to be set are also adhered to given disturbances, for example given fluctuating ambient em or altered atmospheric humidity, with the result that the printing conditions remain the same. It has been shown, however, that print images of the same high print quality are not always produced even given identical printing conditions.
Japanese published application JP-08-058081 A discloses an ink jet printer wherein the moisture content of the print image carrier is acquired. The amount of ink employed for printing is set dependent on the acquired moisture content in order to avoid a xe2x80x9cbleedingxe2x80x9d of the print image.
Japanese Published Application JP-06-115061 A discloses an ink jet printer wherein the amount of ink employed in printing is to be set dependent on the absorbency of the paper, on the permeability or on the surface temperature. A sensor electronically acquires the thickness of the fully saturated paper. Heating resistors that serve for the ejection of ink droplets are driven dependent on the acquired thickness.
German Published Application DE 34 31 484 A1 explained a color ink jet printer wherein, using an optical sensor, a distinction is made between normal paper and a transparent film to be printed. Dependent on the acquired print image carrier, fewer printing points per picture element to be presented are generated in a first operating mode for normal paper than when printing film.
German Letters Patent DE 40 17 850 C1 is directed to a method and an apparatus for regulating the radiation dose of laser radiation when processing materials.
European Patent Document EP-A-0660589 discloses a method for operating a printer, or copier. An input unit is provided in a first exemplary embodiment into which the type of recording medium, for example normal paper, bond paper OHP sheets (overhead paper), smooth paper or recycling paper, is manually input. This input is automated in further exemplary embodiments in that an optical sensor acquires the transmission, the surface condition or the thickness of the recording medium and automatically determines the type of recording medium dependent on the identified values. An optimization of the printing event is then undertaken dependent on the identified type of recording medium in that the illumination level is modified. Further, an adaptation can ensue in view of the hue and the color saturation.
Patent Abstracts of Japan, vol. 1995, no. 09, 31 October 1995 and JP 07 162695 A (Canon, Inc.), 23 Jun. 1995, discloses a color image processor with whose assistance an optimum color balance can be achieved by measuring spectroscopic properties of a recording material. A sensor acquires the light that passes through a recording paper. An RGB sensor measures the color parts of an image of an original master. A computer carries out an RGB correction.
U.S. Pat. No. 5,774,146 discloses an ink printing method with colored ink in order to print a multi-color image. A sensor acquires surface parameters, for example coefficients of friction, the surface roughness, the light reflection of the print paper or a combination thereof. The type of paper employed is then identified on the basis of the sensor signals and printing parameters are defined.
An object of the present invention is to provide printing or, respectively, copying methods wherein the quality of the print images is improved further. Another object of the invention is to provide printer devices that print printed images with high printing quality.
This and other objects of the invention are provided by a method for operating a printer or copier device, whereby at least one optical property of the print image carrier to be printed with a print image is acquired with a sensor, at least one printing parameter is set dependent on the sensor output signal of the sensor, and whereby the print image carrier is printed in a printing event upon employment of the print parameter that has been set step, characterized in that, given a black-and-white printing with gray levels, the gray scale value of the print image carrier is acquired with the assistance of a brightness sensor; and in that at least one printing parameter that influences the generation of the gray levels is set dependent on the output signal of the gray scale value sensor; in that a multi-level character generator is employed when exposing a photoconductor in an electrographic printer or copier device; and in that the illumination energies of the character generator allocated to specific light-coding values are set dependent on the sensor output signal, whereby gray transformation relationships that indicate the illumination energies allocated to the light-coding values dependent on the gray scale value are preferably employed, the gray transformation relationships belonging to specific sensor output signals.
The invention also provides a method for operating a printer or copier device, whereby at least one optical property of the print image carrier to be printed with a print image is acquired with a sensor, at least one printing parameter is set dependent on the sensor output signal of the sensor, and whereby the print image carrier is printed in a printing event upon employment of the print parameter that has been set, characterized in that, given color printing, the color locus of the print image carrier is acquired with the assistance of a color sensor; in that the rated color densities of the colors to be printed are determined with predetermined color transformation relationships that allocate rated color densities for the color separations employed in the printing to the acquired color loci; in that the transformation relationships are empirically determined before the printing event, and are stored as analytical equations or as table in a memory of the printer or, a respectively, copier device.
Further, the invention provides a method for operating a printer or copier device, whereby at least one mechanical property of the print image carrier to be printed with a print image is acquired with a sensor, at least one printing parameter is set dependent on the sensor output signal of the sensor, and whereby the print image carrier is printed in a printing event upon employment of the print parameter that has been set, characterized in that, the roughness of the surface of the print image carrier is acquired with a roughness sensor; in that the toner quantity to be applied onto the print image carrier is set dependent on the output signal of the roughness sensor, whereby the charge potential of a photoconductor collaborating in the printing event and the auxiliary potential of an allocated development station are simultaneously modified. The printing parameters may be modified such that the size of the picture elements of the print image on the print image carrier remains approximately the same.
An additional aspect of the invention provides a method for operating a printer or copier device, whereby at least one optical property of the print image carrier to be printed with a print image is acquired with a sensor, at least one printing parameter is set dependent on the sensor output signal of the sensor, and whereby the print image carrier is printed in a printing event upon employment of the print parameter that has been set, characterized in that the light scatter of the surface of the print image carrier is acquired with an optical sensor; in that printing parameters that determine the raster tonal value or, respectively, the gray scale value and/or the dimensions of fine print details are prescribed dependent on the acquired light scatter; in that a raster toner mark is printed onto the print image carrier; and in that light reflected and/or scattered back in the region of the raster toner mark is acquired with the optical sensor. This aspect is further characterized in that the raster toner mark is applied upon employment of printing parameters that had been previously defined dependent on the gray scale value or color locus of the print image carrier.
In a preferred embodiment, the method is implemented in an electrophotographic printer. Specifically, the illumination energy of an illumination device for exposing a light-sensitive element, an auxiliary potential in a developer unit for the application of toner particles and/or the charge potential of the light-sensitive element are employed as printing parameters. In the method for operating a printer or copier device, the foregoing methods may be utilized in combination.
The invention also provides a printer or copier device, particularly for the implementation of the method, having a printer unit for printing a print image carrier according to predetermined printing parameters, a sensor unit for acquiring at least one optical or mechanical property of the print image carrier to be printed, and a control unit that sets at least one printing parameter dependent on the output signal of the sensor unit, when printing with gray levels, the gray scale value of the print image carrier is acquired with the assistance of a brightness sensor and at least one printing parameter that influences the generation of the gray levels is set dependent on the output signal of the gray scale value sensor given color printing, the color locus of the print image carrier is acquired with the assistance of a color sensor and the rated color densities of the colors to be printed are determined with predetermined color transformation relationships that allocate rated color densities for the color separations employed in the printing to the acquired color loci, and/or in that the roughness of the surface of the print image carrier is acquired with a roughness sensor and the toner quantity to be applied onto the print image carrier is set dependent on the output signal of the roughness sensor; whereby the printing parameters are modified such that the size of the picture elements of the print image on the print image carrier remains approximately the same; and/or the light scatter of the surface of the print image carrier is acquired with an optical sensor; a raster toner mark is preferably printed onto the print image carrier; light reflected or allowed to pass by the raster toner mark is acquired with the optical sensor; and printing parameters that determine the raster tonal value or, respectively, the gray scale value and/or the dimensions of fine print details are prescribed dependent on the acquired light scatter.
The inventive methods are based on the perception that the properties of the print image carrier to be printed critically influence the printing. Print images with constantly high print quality and with constant printed image impression for the viewer on print image carriers having different properties can only be generated when the influences of these properties on the print image are taken into consideration in the printing event. In the inventive method, at least one optical or mechanical property of the print image carrier to be printed is therefore acquired with the assistance of a sensor. At least one printing parameter is then set dependent on the sensor output signal. What this measure achieves is that influences of the type of paper employed, for example yellowish, rough environmental paper instead of white, smooth paper, on the print quality and, thus, on the subjective impression made on the viewer of the print image are taken into consideration and compensated.
In the method according to the present invention, the gray scale value of the print image carrier is acquired with a brightness sensor when printing with gray levels. Moreover, at least one printing parameter that influences the generation of the gray levels is set dependent on the output signal of the gray scale value sensor. For example, the number of gray scale values that is presented given what is referred to as a multi-level character generator, as disclosed by U.S. Pat. No. 5,767,888, is also retained unmodified given print image carriers having a different gray scale value in that the illumination energies allocated to specific light-coding values are set dependent on the output of the brightness sensor. Gray transformation relationships belonging to specific output signals of the brightness sensor are thereby preferably employed, the relationships indicating the illumination energies allocated to the light-coding values being dependent on the gray scale value. What is achieved by modifying the illumination energies is that, independently of the gray scale value of the print image carrier, the same number of gray levels remain distinguishable in the print image because a variation of the gray scale values in the print image is opposed by the gray scale value of the print image carrier. What can be particularly prevented is that a saturation appears given dark gray scale values that makes regions with these gray scale values appear black. The dark gray tones thus remain distinguishable both mensurationally as well as when viewed.
In the method according to a further aspect of the invention, the color locus of the print image carrier is acquired with the assistance of a color sensor given color printing. Subsequently, the rated color densities of the colors to be printed are determined with predetermined color transformation relationships that allocate rated color densities to the acquired color locuss, these assuring that colors that correspond to the colors to be produced on white normal paper are generated in the print image despite the color locus that deviates from white. Full-color images printed on a colored paper thus have the same number of colors that would arise on white paper without the correction. For example, the color densities of the four color separations yellow, magenta, cyan and black are corrected. Similar to the gray scale value, differences in the color locus of the print image carrier lead to a modified number of presented color levels when a saturation given dark colors is not opposed. The differences in the color locus of the print image carrier also influence the hue of the print image when the color transformation relationships are not suitably selected.
In one development, the gray and color transformation relationships are empirically determined before the printing event and are stored in a memory of the printer or, respectively, copier, preferably as analytical equations or as a table. In the empirical determination of the transformation relationships, the corrections of the gray levels or, respectively, of the color separations are evaluated, this being undertaken by an experienced printing technician dependent on the brightness or, respectively, on the color of the paper.
As a critical property of the print image carrier, the roughness of the print image carrier is acquired with the assistance of a roughness sensor given the method according to another aspect of the invention. The amount of toner to be applied onto the print image carrier is influenced dependent on the output signal of the roughness sensor in that, for example given an electrophotographic printing event, the charge potential of the photoconductor and/or the auxiliary potential at the development station is raised or, respectively, lowered. What this measure achieves is that more or fewer toner particles are deposited without modifying the boundaries of the pixels (picture elements). When, for example, the gray tones are generated with the assistance of a rastering step, then fades at the edge of the raster area given rough paper are prevented with a more intense application of toner. The gray scale value, defined as a ratio of covered and non-covered area, remains constant independently of the roughness of the print image carrier.
As a further property of the print image carrier, the light scatter of the print image carrier is acquired with an optical sensor in another development given the method according to yet a further aspect of the invention. Light scatter and gray scale value are different properties of the print image carrier. When, for example, the printer device works with a raster in order to present different gray tones, then the light scatter of the print image carrier is acquired, for example, in that a raster toner mark at which toner-free and toner-covered regions alternate, for example in the fashion of a checkerboard pattern, is printed on the print image carrier. After the raster toner mark is fixed in a fixing station, the raster toner mark is irradiated with light having a predetermined intensity and the light remitted by the raster toner mark is acquired with the optical sensor. The optical sensor covers a region that averages over the light and dark areas of the raster toner mark. The region is selected of such a size that statistical fluctuations in the print image of the raster toner mark do not falsify the result of the acquisition. Printing parameters that determine the raster tone value or, respectively, the gray scale value and/or the dimensioning of fine print structures, for example fine lines, are then set dependent on the acquired light quantity. Given an electrophotographic printing event, for example, the charge potential of the photoconductor is varied given a constant auxiliary potential at the development station. For example, the raster in the raster toner mark has a rastering of 42 xcexcm. When the raster toner mark has a size of approximately 1 cm2, then the light scatter of the print image carrier can be acquired in a simple way because more or less light proceeds under the covered toner regions of the raster and is absorbed thereat dependent on the dispersion properties of the print image carrier.
By acquiring the light quantity with the assistance of a raster toner mark, the gray scale value produced by the print image carrier and by the toner image is also acquired. Since the gray scale value or, respectively, the raster toner value are also dependent on the gray scale value or, respectively, the color value of the surface of the paper, these properties of the carrier material can also be indirectly taken into consideration when the printing parameters are set dependent on the raster toner value determined with the raster mark.
In a development, the raster toner mark is applied upon employment of printing parameters that have been previously defined dependent on the gray location or, respectively, color locus of the print image carrier and/or dependent on the roughness of the print image carrier. In this procedure, the properties having the greatest influence on the print image and, thus, on the impression of a viewer are taken into consideration first. Subsequently, the light scatterxe2x80x94which does not have a negligible influence on the print imagexe2x80x94is taken into consideration.
The invention is also directed to printer or, respectively, copier devices that, in particular, can be employed for the implementation of the inventive methods or their developments. The aforementioned technical effects also apply to the printer or, respectively, copier devices.